Absorbent article having absorbent core including regions of lower density

ABSTRACT

An absorbent article is defined by a pair of opposing longitudinal edges  20;22  and a pair of opposing transverse edges  24;26 . An absorbent core  18  has at least a first  28  and a second  30  region, the average density of the absorbent core  18  in these first and second regions  28, 30  being lower than the average density of the absorbent core  18  surrounding said first and second regions  28;30 , the first and second lower density regions  28;30  being arranged symmetrically about the longitudinal center line A of the article such that each of the first and second lower density regions  28;30  extends to the respective longitudinal edge  20;22  of the absorbent core. The distance a x  varying along the longitudinal direction of the article. A minimum distance a 1  is located at least in the transition  32  between the crotch portion  14  and the front portion  12.

CROSS-REFERENCE FOR RELATED APPLICATIONS

The present application is a continuation of PCT/SE2005/001146, filed onJul. 13, 2005, the entire contents of which are incorporated herein.

FIELD OF THE INVENTION

The present invention relates to absorbent articles, such as sanitarytowels, panty liners, incontinence pads or diapers which are designed sothat they adopt a particular form when in use. Certain regions of thearticle which are less dense than other regions allow the article totake on a desired form and minimise the problems associated with thearticle moving out of place on the user's body.

BACKGROUND TO THE INVENTION

As well as good absorptive properties, primary requirements of absorbentarticles are good fit and comfort. Various methods have been employed inthe design and manufacture of absorbent articles so that they follow thecontours of the user's body well and do not move out of place duringuse.

Patent applications WO 03/053301, EP 0 956 844, WO 03/047484, WO02/087484, WO 02/085270, WO 03/059222, WO 02/087483, WO 02/085269 andrelated applications describe absorbent products which comprise astiffening element that is intended to contribute to thethree-dimensional shape of the products during their use.

EP 1 458 718 describes a disposable diaper having a region of lowstiffness being a rectangular region along each side edge of theabsorbent member. The low bending stiffness of this region allows thediaper to be bent upwards easily to join around the waist of the user.

EP 1 275 358 describes an absorbent article having a front absorbentregion and a rear cushion region. The stiffness is higher in the frontabsorbent region, such that the shape of the raised region ismaintained.

US 2004/0122407 discloses a sanitary napkin, the longitudinal centralregion of which has a higher flexure-resistance than the outer portions.In this way, the side regions are flexible enough that the sanitarynapkin forms a cup-like trough under the wearers' genitals.

EP 0 572 033 discloses an absorbent article having zones which vary instiffness. The article resists bunching and twisting during use. EP 1102 824 discloses a sanitary napkin, the edges of which are less stiffthan the center for comfort.

There is still room for improvement in the comfort and fit of absorbentarticles such as sanitary napkins. In particular, many of the earlierapproaches to this problem involve cutting or otherwise removing partsof the absorbent cores of absorbent articles. However, this reduces thetotal amount of absorbent material which is present and thus provideslower security against leakage. Furthermore, cutting or otherwiseremoving parts of the absorbent core often results in wasted material,as the cut-out parts cannot always be used. Furthermore, many knownproducts require additional stiffening elements.

OBJECTS AND SUMMARY

The present disclosure addresses the problems associated with the priorart in this area. Particularly, it discloses an absorbent article whichcombines the features of softness and comfort with good fit and correct,secure placement of the article on the wearer. Cutting or otherwiseremoving parts of the absorbent core may be avoided, providing moreabsorbent material (and thus higher absorption capacity) and giving thewearer the impression of a more “complete” article (thus improvingwearer confidence). The effects are achieved solely through theabsorbent core of the article, thus avoiding the use of additionalstiffening elements. The articles can also be manufactured usingexisting equipment, with only minor modifications to current processes.

According to a first embodiment, an absorbent article, such as asanitary towel, a panty liner, an incontinence pad or a diaper, saidarticle having transverse and longitudinal directions. The article hasfront, crotch and rear portions. The article comprises an absorbent coreof unitary construction, said absorbent core being defined by a pair ofopposing longitudinal edges and a pair of opposing transverse edges. Theabsorbent core has at least a first and a second region, the averagedensity of the absorbent core in these first and second regions beinglower than the average density of the absorbent core surrounding saidfirst and second regions. The first and second lower density regions arearranged symmetrically about the longitudinal center line of thearticle. The first and second lower density regions extend to therespective longitudinal edges of the absorbent core, and the distancebetween said first and second lower density regions in the transversedirection varies along the longitudinal direction of the article. Aminimum distance between said first and second lower density regions inthe transverse direction is located at least in the transition betweenthe crotch portion and the front portion of the article.

In a further embodiment, the article further comprises a third regionhaving an average density which is lower than the average density of theabsorbent core surrounding said third region, said third lower densityregion being located in the rear portion of the article. This thirdlower density region extends to the transverse edge of the absorbentcore. The third lower density region has an axis of symmetry lying onthe longitudinal center line of the article.

In a third embodiment, the absorbent article is symmetric about thetransverse center line, and the distance between said first and secondlower density regions in the transverse direction has a further minimumlocated in the transition between the crotch portion and the rearportion. The article further comprises a sixth lower density regionhaving an average density which is lower than the average density of theabsorbent core surrounding said sixth region. The sixth lower densityregion is located in the front portion of the article, and extends tothe transverse edge of the absorbent core. The sixth lower densityregion has an axis of symmetry lying on the longitudinal center line ofthe article. Such an article may be placed either way round on the user.

In a fourth embodiment, the absorbent article is symmetric about thetransverse center line and the absorbent core additionally has a fourthand a fifth region. The average density of the absorbent core in thesefourth and fifth regions is lower than the average density of theabsorbent core surrounding said fourth and fifth regions. The fourth andfifth lower density regions are arranged symmetrically about thelongitudinal center line of the article, and extend to the respectivelongitudinal edges of the absorbent core. The distance between thefourth and fifth lower density regions in the transverse directionvaries along the longitudinal direction of the article, and a minimumdistance between said fourth and fifth lower density regions in thetransverse direction is located at least in the transition between thecrotch portion and the rear portion. The article further comprises asixth region having an average density which is lower than the averagedensity of the absorbent core surrounding said sixth region, said sixthlower density region being located in the front portion of the articleand extending to the transverse edge of the absorbent core. The sixthlower density region has an axis of symmetry lying on the longitudinalcenter line of the article.

Preferably, the maximum extension of the first and second lower densityregions in the longitudinal direction is less than the total extensionof the absorbent article in the longitudinal direction. Suitably, themaximum extension of the first and second lower density regions b_(x) inthe longitudinal direction is between 3-10 cm, more preferably between4-8 cm, most preferably between 5-7 cm.

Similarly, the maximum extension of the third lower density region inthe transverse direction may be less than the total extension of theabsorbent article in the transverse direction. The maximum extension ofthe third lower density region in the transverse direction is suitablyless than 75%, more preferably less than 50%, most preferably less than25% of the total extension of the absorbent article in the transversedirection.

In the absorbent article, the distance between the first and secondlower density regions in the transverse direction of the article ispreferably greater at the crotch point of the article than in thetransition between the crotch portion and the front portion.

In one embodiment, the first, second, third and any further lowerdensity regions have a lowest density which is at least 20% lower, morepreferably at least 30% lower and most preferably at least 50% lowerthan the density of the absorbent core surrounding these regions. Inanother embodiment, the density of the first, second, third and anyfurther lower density regions varies such that it increases graduallytowards the edges of said regions, and reaches 100% of the density ofthe absorbent core surrounding these regions, at the edges of theregions where they meet the remainder of the absorbent core.

The minimum distance between said first and second lower density regionsin the transverse direction, located in the transition between thecrotch portion and the front portion is preferably between 15 and 45 mm,more preferably between 20 and 30 mm.

The absorbent article may further comprise lines or markings on thewearer-facing side of the absorbent core which indicate the location ofthe lower density areas.

In addition to the absorbent core, the absorbent article may furthercomprise an inner coversheet and an outer coversheet. Suitably, theabsorbent core is not joined to the outer coversheet in any of the lowerdensity regions. The minimum total thickness of the article ispreferably at least 3 mm, more preferably at least 5 mm. Preferably, thethickness of the absorbent core is substantially uniform across itslongitudinal and transverse directions.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an embodiment of the invention which is a sanitary towel.

FIG. 2 shows an alternative arrangement of the lower density regions inan absorbent article.

FIG. 3 shows another arrangement of the lower density regions in anabsorbent article.

FIG. 4 shows another arrangement of the lower density regions in anabsorbent article.

FIGS. 5, 6, 7 and 8 are cross-sectional views of methods by whichabsorbent cores of the present invention may be produced.

DETAILED DESCRIPTION OF THE INVENTION PREFERRED EMBODIMENTS

An absorbent article 10, may be a sanitary towel, a panty liner, anincontinence pad or a diaper. Preferably, the absorbent article 10 is asanitary towel. Such articles are commonly used for acquisition andstorage of bodily exudates such as urine, faeces or menstrual fluid. Theabsorbent article is preferably disposable—i.e. it is intended to beused only once and disposed thereafter, rather than being cleaned andre-used.

FIG. 1 shows an embodiment of the present invention which is a sanitarytowel. The article has transverse (x) and longitudinal (y) directions asindicated. The total length of the article in the transverse directionis length a, while the total length of the article in the longitudinaldirection is length b.

The article further has front 12, crotch 14 and rear 16 portionsarranged in the article's longitudinal direction. In use, the frontportion 12 of the article is intended to cover the pubic region of thewearer. The front portion 12 is defined by the front transverse edge ofthe article and extends a certain length b1 along the article in thelongitudinal direction. In a sanitary napkin of the type shown, thefront portion 12 has a length b1 in the longitudinal direction which isbetween 10-50%, more preferably between 25-40%, most preferably between30-35% of the total length b of the article.

The crotch portion 14 of the article is located adjacent to the frontportion 12 in the longitudinal direction. In use, the crotch portionlies between the legs of the user and covers the user's genital regionand perineum. In a sanitary napkin of the type shown, the crotch portion14 has a length b2 in the longitudinal direction which is between10-50%, more preferably between 25-40%, most preferably between 30-35%of the total length b of the article. Typically, the length b2 of thecrotch portion 14 in the longitudinal direction is between 40-110 mm,more preferably between 50-105 mm, most preferably between 85-100 mm.The transition 32 between the front portion 12 and the crotch portion 14is the border area between the front and crotch portions.

The rear portion 16 is located at the opposite end of the article fromthe front portion 12 and is located adjacent to the crotch portion 14 inthe longitudinal direction. In use, the rear portion 16 extends towardsthe user's rear. The rear portion 16 is defined by the rear transverseedge of the article and extends a certain length b3 along the article inthe longitudinal direction. In a sanitary napkin of the type shown, therear portion 16 has a length b3 in the longitudinal direction which isbetween 10-50%, more preferably between 25-40%, most preferably between30-35% of the total length b of the article.

In addition to the absorbent core 18 described herein, absorbentarticles typically comprise an inner coversheet 48 and an outercoversheet 50. The inner coversheet 48 lies in direct contact with thewearer's body, and should therefore be soft, comfortable andliquid-permeable. The inner coversheet can comprise a nonwoven material,e.g. spunbond, meltblown, carded, hydroentangled, wetlaid etc. Suitablenonwoven materials can be composed of natural fibres, such as wood pulpor cotton fibres, manmade fibres, such as polyester, polyethylene,polypropylene, viscose etc. or from a mixture of natural and man-madefibres. The inner coversheet material may further be composed of twofibres, which may be bonded to each other in a bonding pattern, as e.g.disclosed in EP-A-1 035 818. Further examples of inner coversheetmaterials are porous foams, apertured plastic films etc. The materialssuited as inner coversheet materials should be soft and non-irritatingto the skin and be readily penetrated by body fluid, e.g. urine ormenstrual fluid. The inner coversheet may further be different indifferent parts of the absorbent article.

The outer coversheet 50 lies in contact with the wearer's garments, andis liquid-impermeable. The outer coversheet refers to the liquidimpervious material forming the outer cover of the absorbent article.The outer coversheet can comprise a thin plastic film, e.g. apolyethylene or polypropylene film, a nonwoven material coated with aliquid impervious material, a hydrophobic nonwoven material, whichresists liquid penetration, or a laminate of a plastic film and anonwoven material. Other laminate materials which are suitable for useas the outer coversheet are laminates of a nonwoven material andhigh-loft wadding material. The outer coversheet material may bebreathable so as to allow vapour to escape from the absorbent core,while still preventing liquids from passing therethrough. Examples ofbreathable outer coversheet materials are porous polymeric films,nonwoven laminates of spunbond and meltblown layers and laminates ofporous polymeric films and nonwoven materials. Preferably, the outercoversheet comprises nonwoven material in at least the garment-facingsurface thereof.

In an alternative embodiment, the absorbent article 10 may only comprisean outer coversheet. Additionally, the absorbent core 18 of theabsorbent article may be wrapped in a single coversheet which can act asboth inner and outer coversheet.

In one embodiment, the absorbent core 18 is not joined to the outercoversheet 50 in any of the lower density regions. This allows theabsorbent core 18 and the inner and outer coversheets of the article todeform independently of each other. The inner and outer coversheets donot therefore hinder the deformation of the absorbent core. The articlefollows the contours of the user's body more closely and provides thearticle with greater flexibility.

The absorbent article may further include an acquisition distributionlayer (not shown) which is placed on top of the absorbent core andadapted to quickly receive and temporarily store discharged liquidbefore it is absorbed by the absorbent core. Such acquisitiondistribution layers are well known in the art and may be composed ofporous fibrous wadding, SD plastic film, LDA (low density airlaid),multibond, latex bonded or foam materials.

The absorbent article 10 of the invention comprises an absorbent core 18of unitary construction. The “absorbent core” is the absorbent structureof the article which acquires and stores bodily fluids. The absorbentcore can be of any conventional kind. Examples of commonly occurringabsorbent materials are cellulosic fluff pulp, tissue, highly absorbentpolymers (so called superabsorbents), absorbent foam materials,absorbent nonwoven materials or the like. It is common to combinecellulosic fluff pulp with superabsorbent polymers in an absorbent core.

Superabsorbent polymers are water-swellable, water-insoluble organic orinorganic materials capable of absorbing at least about 20 times theirown weight of an aqueous solution containing 0.9 weight percent ofsodium chloride. Organic materials suitable for use as a superabsorbentmaterial can include natural materials such as polysaccharides,polypeptides and the like, as well as synthetic materials such assynthetic hydrogel polymers. Such hydrogel polymers include, forexample, alkali metal salts of polyacrylic acids, polyacrylamides,polyvinyl alcohol, polyacrylates, polyacrylamides, polyvinyl pyridines,and the like. Other suitable polymers include hydrolyzed acrylonitrilegrafted starch, acrylic acid grafted starch, and isobutylene maleicanhydride copolymers and mixtures thereof. The hydrogel polymers arepreferably lightly cross-linked to render the material substantiallywater insoluble. Preferred superabsorbent materials are further surfacecross-linked so that the outer surface or shell of the superabsorbentparticle, fibre, flake, sphere, etc. possesses a higher crosslinkdensity than the inner portion of the superabsorbent. The superabsorbentmaterials may be in any form suitable for use in absorbent compositesincluding particles, fibres, flakes, spheres, and the like. A highabsorption capacity is provided by the use of high amounts ofsuperabsorbent material.

The thin absorbent bodies, which are common in for example baby diapersand incontinence guards, often comprise a compressed, mixed or layeredstructure of cellulosic fluff pulp and superabsorbent polymers. The sizeand absorbent capacity of the absorbent core may be varied to suitdifferent uses, such as infants or adult incontinent persons.

The phrase “unitary construction” in the present context is intended tomean that the absorbent core 18 is constructed from essentially one typeof material, this being essentially the same material, or essentiallythe same combination of two or more materials throughout the absorbentcore. Variations in density and concentration of the material may occur,but these are limited to those which can be obtained withoutincorporation of regions which have been formed separately and thenphysically joined to each other. For example, when the absorbent corecomprises a matrix of hydrophilic fibres and superabsorbent material asdescribed above, the relative concentrations of superabsorbent materialand fibres may be different in different parts of the core. However, theabsorbent core should not, for instance, comprise layers or laminates ofdifferent composition. Likewise, variations in the density orconcentration of various components across the longitudinal ortransverse directions of the absorbent core are acceptable, yet the coreshould not comprise areas or layers of different composition which areformed separately and later joined together.

A suitable technique for forming the absorbent cores of the presentinvention is mat-forming through an air-laying process, as illustratedin FIGS. 5 a-c and as described more closely in EP-A2-1 253 231. Anair-permeable mould 52 having the desired shape is provided. The depthof the mould can vary, as seen in the cross-sectional view in FIG. 5 a,according to the amount of material which is required at each point.Fibrous material 54 is air-laid into the mould, and the mould is filled(see FIG. 5 b). Due to the differences in the mould depth in variousareas, the amount of fibrous material at each point will vary (FIG. 5c).

After the absorbent core is produced, it is compressed so that a uniformthickness across the entire core (i.e. in the longitudinal andtransverse directions) is obtained (see FIG. 5 d). Compressing may takeplace using any known means, but a smooth roll is usually sufficient toobtain the desired thickness. Accordingly, in one embodiment, theabsorbent core has substantially uniform thickness across itslongitudinal (y) and transverse (x) directions. By “uniform thickness”is meant that the thickness of the absorbent core is the same across theentire core.

In this way, areas of different densities can be built up within theabsorbent core. If desired, masks or baffles may be introduced in themat-forming process, so that fibre-laying in the unmasked areas ishigher than in the masked areas. Alternatively, the moulds may havedifferent hole density and/or hole size in different areas of the mould.The flow of fibrous material will therefore be different in differentareas of the mould. This allows further control over the materialdensity.

In the efficient mat-forming processes of today, mat-forming wheels areused, as described in U.S. Pat. No. 4,765,780, SE 9401542-7 and EP-A2-1253 231. The air-permeable moulds are evenly spaced about the peripheryof the mat-forming wheels. Fibrous material (together with any othermaterial which might be desired) is fed from mills by means of blowersand onto mat-forming wheels via mat-forming covers. More than onemat-forming cover may be present per forming wheel.

In an alternative to forming in mat-forming wheels, the absorbent coresof the present invention may be produced by laying fibrous material(together with any other material which might be desired) onto a webhaving a profile which ultimately gives a density difference ondifferent parts of the material web. The material can be prefabricatedand rolled up into rolls.

The absorbent core 18 produced according to this method appears to beunitary, as the location of the lower density regions is not visible tothe eye. This provides the wearer with a greater sense of security.However, the absorbent article 10 may further comprise lines or markings46 on the wearer-facing side of the absorbent core 18. In this way,correct placement of the article is promoted and the location of thelower density areas is indicated. The lines or markings 46 can becompressed lines which form folding lines on the article and promotecorrect folding of the article when worn.

A further process through which absorbent cores having the selectedlower density regions is shown in FIGS. 6 a-d. As above, fibrousmaterial 54 is air-laid into a mould 52 having variable depth (FIG. 6 a,6 b). A core is thus formed which has variable thickness, being thinnerin the regions in which lower density is desired (FIG. 6). In contrastwith the above, the core is then compressed with a profiled roll, suchthat different thicknesses are obtained over the extent of the core; thethickest areas being those in the areas which lie outside the desiredareas of lower density (FIG. 6 d).

An alternative method for obtaining an absorbent core according to thepresent invention is illustrated in FIGS. 7 a-b. In this embodiment,fibrous material 54 is formed with a uniform thickness, having a densitywhich corresponds to the density of the absorbent core surrounding theregions of lower density (i.e. the higher density). Such a “higher”density may be present from the beginning, when the material is layed,or may be obtained through compressing a material of lower density.Lower density regions of the absorbent core may then be achieved throughtreatment of the absorbent core in those regions in which lower densityis desired. One example of such treatment uses ionising radiation, asdescribed in patent application WO2004/044325. Alternatively, chemicalor mechanical treatment of the absorbent core may also provide thedesired density in the lower density regions. Combinations of radiation,chemical and mechanical treatment can also be used to obtain lowerdensity absorbent cores. The person skilled in the art will be able toapply the most suitable technique for each absorbent core and productionmethod. Mechanical treatment of an absorbent core after formation willprovide higher bulk. This change in thickness contributes to increasedsecurity against leakage, as the lower density material which resultshas a lower capillary action. A transport gradient is thereby provided,in which absorbed liquid tends to flow away from the thicker areas.

Variations in the extent of compression can also provide an absorbentcore having desired lower density regions (FIGS. 8 a-b). In thisembodiment, fibrous material 54 is formed with a uniform thickness,having a density which corresponds to the density of the absorbent corein the regions of lower density. The absorbent core outside theseregions is then compressed, while within these regions, the core remainsuncompressed (FIG. 8 b).

The absorbent core 18 is defined by a pair of opposing longitudinaledges 20;22 and a pair of opposing transverse edges 24;26. The absorbentcore does not necessarily have a parallelogram shape, but may have e.g.rounded edges or a dog-bone shape. In this case, the transition betweentransverse and longitudinal edges is defined as the point on the edge ofthe article at which the rate of curvature of the transverse edge of thearticle with respect to the transverse direction is greatest. In apreferred embodiment, the longitudinal edges of the article aresubstantially parallel.

The absorbent core 18 has a lower density in at least a first 28 and asecond region 30. That is, the first and second regions 28,30 have anaverage density which is lower than the average density of the absorbentcore surrounding these regions.

The first and second lower density regions 28;30 are arrangedsymmetrically about the longitudinal center line A of the article. Thisis so that the article lies symmetrically on the user's body when inuse. By “arranged symmetrically” is meant each point in the first lowerdensity region 28 has a corresponding point in the second lower densityregion 30; the two points being related to each other by reflection in aplane located on the longitudinal center line A of the article. Thefirst and second lower density regions 28;30 are therefore mirror imagesof each other and are located in corresponding locations on oppositesides of the longitudinal center line A.

The first and second lower density regions 28;30 extend to therespective longitudinal edges 20;22 of the absorbent core. The distancea_(x) between the first and second lower density regions 28;30 in thetransverse direction of the absorbent article varies along thelongitudinal direction of the article. That is, the edge of the first orsecond lower density regions 28;30 lying closest to the longitudinalcenter line A of the article is not parallel with this longitudinalcenter line A. The distance a_(x) therefore exhibits maxima and minimaalong the longitudinal direction of the article. Preferably, thedistance a_(x) varies continuously along the longitudinal direction ofthe article.

A minimum distance a₁ between said first and second lower densityregions 28;30 in the transverse direction is located at least in thetransition 32 between the crotch portion 14 and the front portion 12.The distance between the lower density regions 28;30 may exhibit morethan one minima, but preferably, there is one minimum distance a₁, whichlies in the transition 32.

The area around the crotch in which an absorbent article lies is definedin particular by two muscle tendons which are located down either sideof the groin. These muscle tendons form part of the muscle group whichoriginates on the inside of the pelvic diaphragm and has its attachmentalong the thigh. The muscle group consists of the adductor brevis,adductor longus, gracilis and adductor magnus muscles. In use,therefore, the absorbent article is placed between these muscle tendons,and the first and second lower density regions 28;30 are located betweensaid tendons and compressed by them. Thus the term “transition betweenthe crotch portion and the front portion” is herein defined as theregion which in the intended use of the article is located between thesetwo muscle tendons.

In that a minimum distance a₁ between said first and second lowerdensity regions 28;30 in the transverse direction is located at least inthe transition 32 between the crotch portion 14 and the front portion12, the transition 32 is held correctly between these two tendons. Thefront portion 12 of the article is therefore held in the area in frontof these tendons, while the crotch portion 14 of the article ispositioned correctly against the genitals of the wearer. This helps toavoid problems associated with incorrect placement of the absorbentarticle, or movement of the article during wear. In particular, legmovements of the wearer often cause conventional sanitary towels to movebackwards, which may be reduced by the present invention.

The distance between the two muscle tendons in the crotch of the wearer,which has been shown to be relatively constant for all people, is around25-45 mm. In around 80% of women, the distance between these two tendonsis approximately 30-32 mm. The minimum distance a₁ between said firstand second lower density regions 28;30 in the transverse direction istherefore preferably between 15 and 45 mm, more preferably between 20and 30 mm. If the distance a₁ exceeds ca. 35 mm, the article is likelyto feel uncomfortable for the majority of wearers. If the distance a₁exceeds 45 mm, discomfort and chafing is highly likely to occur. Notethat it is preferable that the minimum distance a₁ between said firstand second lower density regions 28;30 in the transverse directionshould be greater than zero. In a preferred embodiment, the first andsecond lower density regions do not overlap in the transverse direction.

Compression of the first and second lower density regions 28;30 of theabsorbent article 10 in the transverse direction between the tendons inthe inner thigh of the wearer also promotes formation of the correct3-dimensional form of the article. In particular, transverse compressionof the longitudinal edges 20;22 at the lower density portions allows thefront portion 12 of the article to fold upwards towards the user, and a“bowl” shape can be formed. This allows closer, more secure fit of thearticle. Predetermined shaping of the absorbent article also reduces therisk of the article folding in an undesired manner, for example creatingchannels which may cause leakage.

After production, absorbent articles of the kind described herein areusually folded and packaged. Further advantages of the inventiveabsorbent article are evident upon folding and packaging. As the articleis substantially planar when not in use, folding and packaging of theabsorbent article are simplified as compared to a three-dimensionalarticle. Additionally, any creases or folds which are introduced whenthe article is packaged can remain present after the article has beenremoved from the packaging. This presents problems when the article isto be worn, as these residual creases or folds from the packagingprocess may cause the article to fold in an undesirable manner when inuse, and may also form channels in the article along which liquid caneasily run, increasing the likelihood of leakage. Introducing the lowerdensity regions reduces the tendency of the article to retain creases orfolds from the packaging process after being removed from the packagingand, as these lower density regions lie at the edges of the absorbentcore of the article, the transport gradient tends to promote liquid flowaway from the edges. In effect, any folds which exist in the articleafter the packaging has been opened are limited by the lower densityareas.

A further effect of the areas of lower density is that they have largerpores and capillaries and therefore lower capillary action than thesurrounding areas. A capillary gradient is therefore present in thearticle, so that liquid is absorbed more preferentially into the denser(non-soft) areas. This leads to an article having improved securityagainst leakage, as liquid will not be distributed into the lowerdensity areas as much as the denser areas.

In the embodiment shown in FIG. 2, the article further comprises a thirdregion 34 having an average density which is lower than the averagedensity of the absorbent core 18 surrounding said third region 34. Thislower density third region 34 is located in the rear portion 16 of thearticle and extends to the transverse edge 26 of the absorbent core.Again, to maintain symmetry of the article, the third lower densityregion 34 should have an axis of symmetry A1 which lies on thelongitudinal center line A of the article. The third lower densityregion 34 may take any shape, as long as it is symmetrical about thelongitudinal center line A of the article. A triangular shape as shownin FIG. 2 is particularly suitable for the third lower density region34.

By means of this embodiment, the comfort and fit of the absorbentarticle are further increased. The absorbent article folds along thelongitudinal center line A in the rear portion, and is thus accommodatedin the cleft between the user's buttocks. This reduces the risk ofleakage from the rear of the article. Furthermore, the third lowerdensity region 34 introduces an absorption gradient in the rear portionof the article which deters liquid flow through this rear portion.Promoting a certain fold line in the rear portion increases the comfortof absorbent articles, as undesired twisting, bunching or Z-folding ofthe article between the buttocks is reduced. Folding of the rear portion16 between the user's buttocks also promotes secure fit, as transverseand longitudinal movement of the article during wear is reduced. Thethird lower density region 34 in the rear portion 16 cooperates with thefirst and second lower density regions 28;30 to provide the article witha form which follows the contours of the wearer's body even moreclosely.

In the embodiment shown in FIG. 3, the article is symmetrical about thetransverse center line B (i.e. the front and rear portions 12;16 are thesame size and shape, and have the same length in the longitudinaldirection). The article can therefore be placed upon the wearer ineither direction. For this to occur, the distance a_(x) between thefirst and second lower density regions 28;30 in the transverse directionexhibits a further minimum value a₃ which is located in the transition32 between the crotch portion 14 and the rear portion 16. The articlefurther comprises a sixth region 38 having an average density which islower than the average density of the absorbent core 18 surrounding saidsixth region 38. The sixth lower density region 38 is located in thefront portion 12 of the article, and extends to the transverse edge 24of the absorbent core. As with the third lower density region 34, saidsixth lower density region 38 must also have an axis of symmetry A1lying on the longitudinal center line A of the article. The article canthus be worn in either direction with the same good results.

FIG. 4 shows an alternative way of obtaining an article which can beplaced either way around on the user. Instead of the first and secondlower density regions 28;30 extending into the transition 32 between thecrotch portion 14 and the rear portion 16, the article additionally hasa fourth 40 and a fifth 42 region, the average density of the absorbentcore 18 in these fourth and fifth regions 40, 42 being lower than theaverage density of the absorbent core 18 surrounding said fourth andfifth regions 40;42. These fourth and fifth lower density regions 40;42are arranged symmetrically about the longitudinal center line A of thearticle and extend to the respective longitudinal edges 20;22 of theabsorbent core 18. In a similar way to above, the distance a_(y) betweenthe fourth and fifth lower density regions 40;42 in the transversedirection varies along the longitudinal direction of the article. Aminimum distance a₄ between said fourth and fifth lower density regions40;42 in the transverse direction is located at least in the transition32 between the crotch portion 14 and the rear portion 16. As above, thearticle further comprises a sixth region 38 having an average densitywhich is lower than the average density of the absorbent core 18surrounding said sixth region 38. This sixth lower density region 38 islocated in the front portion 12 of the article, and extends to thetransverse edge 24 of the absorbent core. This sixth lower densityregion 38 has an axis of symmetry A1 lying on the longitudinal centerline A of the article. The article according to this embodiment can beworn in either direction with the same good results.

The first and second lower density regions 28;30 have an extension alongthe article in the longitudinal direction. Increasing the longitudinalextension of these lower density regions provides the article with softedges, which further increases comfort. However, the minimum distance a₁between the first and second lower density regions 28;30 in thetransverse direction should be at least in the transition 32 between thecrotch portion 14 and the front portion 12. Preferably, the first andsecond lower density regions 28;30 do not extend along the entire lengthof the article in the longitudinal direction; i.e. the maximum extensionb_(x) of the first and second lower density regions 28;30 in thelongitudinal direction y is less than the total extension b of theabsorbent article in the longitudinal direction y. Suitably, the maximumextension b_(x) of the first and second lower density regions 28;30 inthe longitudinal direction y is between 3-10 cm, more preferably between4-8 cm, most preferably between 5-7 cm.

In a similar manner, the maximum extension a₂ of the third lower densityregion 34 in the transverse direction x should be less than the totalextension a of the absorbent article in the transverse direction x. Themaximum extension a₂ of the third lower density region 34 in thetransverse direction x is less than 75%, more preferably less than 50%,most preferably less than 25% of the total extension a of the absorbentarticle in the transverse direction x.

The absorbent core 18 of the article preferably does not have lowerdensity at the “crotch point” of the article, as such lower densityusually results in (undesirable) lower absorption properties. In thiscase, distance a_(x) between said first and second lower density regions28;30 in the transverse direction of the article is higher in the crotchpoint 44 of the article than in the transition 32 between the crotchportion 14 and the front portion 12. The “crotch point” is as defined inEP-B1-0 969 784 and described further in international applicationPCT/SE2004/001759. It is determined by placing the article on the wearerin a standing position, and then placing an extensible filament aroundthe legs of the wearer in a figure-of-eight configuration. The point onthe article corresponding to the point of intersection of the filamentis deemed to be the crotch point 44. It should be understood that thecrotch point is determined by placing the absorbent article on thewearer in the intended manner and determining where the crossing pointof the filament would cross the article/core.

Preferably, the first 28, second 30, third 34 and any further lowerdensity regions have a lowest density which is at least 20% lower, morepreferably at least 30% lower and most preferably at least 50% lowerthan the density of the absorbent core surrounding these regions. Thatis, they comprise up to 50% less material at the same degree ofcompression. The density of the absorbent core surrounding the lowerdensity regions should lie between 40-200 kg/m³, preferably between50-200 kg/m³, more preferably between 70-90 kg/m³. This allows thedesired effects to be obtained while maintaining the absorptioncapacity.

The lower density regions may have a variable density which increasesgradually towards the edges of said regions, such that it reaches 100%at the edges of the regions where they meet the remainder of theabsorbent core. In this way, the resistance to stress of the first andsecond regions 28;30 increases as they are compressed. This allows awider range of fit, as users with a narrower crotch will be able tocompress the lower density regions more, while those with wider crotcheswill compress the lower density regions less. The articles willtherefore fit the minority of people who do not have the above-mentionedranges of the distance between the two muscle tendons. Additionally, thedensity gradient in these regions results in an absorption gradient, aslower density material has a lower capillary action. This providesadditional security against leakage, as the absorption properties of thearticle decreases in the lower density regions towards the edges andfluid is directed towards the center of the article.

The various lower density regions 28, 30, 34, 38, 40, 42 may all havethe same density. Alternatively, higher comfort may be provided by anabsorbent article in which the lower density regions extending to thetransverse edges—i.e. the third lower density region 34 and the sixthlower density region 38—have a lower density than the other regions. Inuse, the third or sixth lower density regions 34, 38 are located betweenthe buttocks of the user, so that increased softness in these regions isdesirable.

Material should be present in the lower density regions—the situation inwhich the density of the lower density areas is zero is not comprisedwithin the scope of this invention.

A number of methods for measuring the density of absorbent cores, or theaverage density of samples, have been described in the literature. Inparticular, the average density of a sample of absorbent core may bemeasured according to the following procedure:

-   -   The absorbent article is carefully delaminated: any inner or        outer coversheets are removed so as to only leave a unitary        core.    -   A pressure of 0.5 kPa is applied to the absorbent core via a        foot which corresponds in area to the area of the sample of        absorbent core for which the density is to be measured    -   The thickness of the sample is measured while subject to this        pressure.    -   The samples for which densities are to be calculated are cut out        from the core, and the surface weight (g/cm²) of these samples        is calculated from their mass/surface area.    -   From the surface weight and the thickness, the average density        of these areas is calculated. The average density (kg/m³) is        calculated by dividing the surface weight by the thickness.

A sanitary towel may comprise any attachment means known in the art toallow fastening to undergarments of a wearer. Such means may include acoating of adhesive or friction coating on the garment-facing surface ofthe article, or attachment flaps (“wings”) which extend in thetransverse direction of the article and fold over the crotch portion ofa user's undergarment. It is however important that the nature andplacement of such attachment means does not significantly interfere withthe function of the article in use.

The present invention is particularly relevant to relatively thickabsorbent articles, such as relatively thick sanitary towels, in thatthey are bulky from the beginning and can give a close fit to the body.Such “thick” articles have a thickness lying between around 3 to around12.5 mm, preferably 5-11 mm. However, they do not always fold in therequired manner. The lower density regions of the present inventionallow folding of the article to be directed, without bulky,uncomfortable edges being formed. The minimum thickness of a “thick”article according to the invention should be at least 3 mm, preferablyat least 5 mm.

Although the above discussion has been exemplified through a sanitarynapkin, the present invention is also applicable to other absorbentarticles such as diapers, incontinence pads or panty-liners. Forinstance, application of the invention to diapers would provide similarbenefits in terms of comfort, fit and leakage-prevention.

The invention should not be considered as limited by the abovedescription; rather the scope and limitations of the invention aredefined by the enclosed claims, and equivalents thereof.

The invention claimed is:
 1. An Absorbent article comprising transverseand longitudinal directions, said article further having front, crotchand rear portions, said article comprising an absorbent core of unitaryconstruction, said absorbent core being defined by a pair of opposinglongitudinal edges and a pair of opposing transverse edges, saidabsorbent core having at least a first region and a second region, anaverage density of the absorbent core in these first and second regionsbeing lower than an average density of the absorbent core surroundingsaid first and second regions, said first and second lower densityregions being arranged symmetrically about a longitudinal center line ofthe article and extending to the respective longitudinal edges of theabsorbent core, a distance between said first and second lower densityregions in the transverse direction varying along the longitudinaldirection of the article, and a minimum distance between said first andsecond lower density regions in the transverse direction is located atleast in a transition between the crotch portion and the front portionof the article, wherein a region having the average density of theabsorbent core is disposed along an entire distance of a transverse lineconnecting the first and second lower density regions.
 2. The absorbentarticle according to claim 1, further comprising a third region havingan average density which is lower than the average density of theabsorbent core surrounding said third region, said lower density thirdregion being located in the rear portion of the article, and extendingto the rear transverse edge of the absorbent core, said third lowerdensity region having an axis of symmetry lying on the longitudinalcenter line of the article.
 3. The absorbent article according to claim2, wherein the absorbent article is symmetric about the transversecenter line, and the distance between said first and second lowerdensity regions in the transverse direction has a further minimumlocated in the transition between the crotch portion and the rearportion and said article further comprises a sixth region having anaverage density which is lower than the average density of the absorbentcore surrounding said sixth region, said sixth lower density regionbeing located in the front portion of the article, and extending to thefront transverse edge of the absorbent core, said sixth lower densityregion having an axis of symmetry lying on the longitudinal center lineof the article.
 4. The absorbent article according to claim 1, wherein,the absorbent article is symmetric about the transverse center line andsaid absorbent core having a fourth and a fifth region, the averagedensity of the absorbent core in these fourth and fifth regions beinglower than the average density of the absorbent core surrounding saidfourth and fifth regions, said fourth and fifth lower density regionsbeing arranged symmetrically about the longitudinal center line of thearticle and extending to the respective longitudinal edges of theabsorbent core, the distance between said fourth and fifth lower densityregions in the transverse direction varying along the longitudinaldirection of the article, and that a minimum distance between saidfourth and fifth lower density regions in the transverse direction islocated at least in the transition between the crotch portion and therear portion and said article further comprises a sixth region having anaverage density which is lower than the average density of the absorbentcore surrounding said sixth region, said sixth lower density regionbeing located in the front portion of the article, and extending to thefront transverse edge of the absorbent core, said sixth lower densityregion having an axis of symmetry lying on the longitudinal center lineof the article.
 5. The absorbent article according to claim 1, whereinthe maximum extension of the first and second lower density regions inthe longitudinal direction is less than the total extension of theabsorbent article in the longitudinal direction.
 6. The absorbentarticle according to claim 4, wherein the maximum extension of the firstand second lower density regions in the longitudinal direction isbetween 3-10 cm.
 7. The absorbent article according to claim 4, whereinthe maximum extension of the first and second lower density regions inthe longitudinal direction is between 4-8 cm.
 8. The absorbent articleaccording to claim 4, wherein the maximum extension of the first andsecond lower density regions in the longitudinal direction is between5-7 cm.
 9. The absorbent article according to claim 2, wherein themaximum extension of the third lower density region in the transversedirection is less than the total extension of the absorbent article inthe transverse direction.
 10. The absorbent article according to claim2, wherein the maximum extension of the third lower density region inthe transverse direction is less than 75% of the total extension of theabsorbent article in the transverse direction.
 11. The absorbent articleaccording to claim 2, wherein the maximum extension of the third lowerdensity region in the transverse direction is less than 50% of the totalextension of the absorbent article in the transverse direction.
 12. Theabsorbent article according to claim 2, wherein the maximum extension ofthe third lower density region in the transverse direction is less than25% of the total extension of the absorbent article in the transversedirection.
 13. The absorbent article according to claim 1, wherein thedistance between said first and second lower density regions in thetransverse direction of the article is greater at the crotch point ofthe article than in the transition between the crotch portion and thefront portion.
 14. The absorbent article according to claim 2, whereinthe first, second, third and any further lower density regions have alowest density which is at least 20% lower than the density of theabsorbent core surrounding these regions.
 15. The absorbent articleaccording to claim 2, wherein the first, second, third and any furtherlower density regions have a lowest density which is at least 30% lowerthan the density of the absorbent core surrounding these regions. 16.The absorbent article according to claim 2, wherein the first, second,third and any further lower density regions have a lowest density whichis at least 50% lower than the density of the absorbent core surroundingthese regions.
 17. The absorbent article according to claim 1, whereinthe absorbent article is a sanitary towel, a panty liner, anincontinence pad, or a diaper.
 18. The absorbent article according toclaim 1, wherein the first and second lower density regions are arrangedsymmetrically with respect to each other about the longitudinal centerline of the article.
 19. An Absorbent article comprising transverse andlongitudinal directions, said article further having front, crotch andrear portions, said article comprising an absorbent core of unitaryconstruction, said absorbent core being defined by a pair of opposinglongitudinal edges and a pair of opposing transverse edges, saidabsorbent core having at least a first region and a second region, anaverage density of the absorbent core in these first and second regionsbeing lower than an average density of the absorbent core surroundingsaid first and second regions, said first and second lower densityregions being arranged symmetrically about a longitudinal center line ofthe article and extending to the respective longitudinal edges of theabsorbent core, a distance between said first and second lower densityregions in the transverse direction varying along the longitudinaldirection of the article, and a minimum distance between said first andsecond lower density regions in the transverse direction is located atleast in a transition between the crotch portion and the front portionof the article, wherein said absorbent core has only the said first andsecond regions having an average density lower than the average densityof the absorbent core surrounding first and second regions.
 20. AnAbsorbent article comprising transverse and longitudinal directions,said article further having front, crotch and rear portions, saidarticle comprising an absorbent core of unitary construction, saidabsorbent core being defined by a pair of opposing longitudinal edgesand a pair of opposing transverse edges, said absorbent core having atleast a first region and a second region, an average density of theabsorbent core in these first and second regions being lower than anaverage density of the absorbent core surrounding said first and secondregions, said first and second lower density regions being arrangedsymmetrically about a longitudinal center line of the article andextending to the respective longitudinal edges of the absorbent core, adistance between said first and second lower density regions in thetransverse direction varying along the longitudinal direction of thearticle, and a minimum distance between said first and second lowerdensity regions in the transverse direction is located at least in atransition between the crotch portion and the front portion of thearticle, wherein said absorbent core has only two to six regions havingan average density lower than an average density of the absorbent coresurrounding said two to six regions.